It is known to use rectifiers in order to entirely or partially constitute circuits which transform an alternating voltage produced by a voltage generator into a direct-current voltage suitable for supplying power to electronic circuitry: such a rectifier is known from the document WO 85/01161 which describes a rectifier according to the preamble of claim 1. Such circuits are used, for example, in wristwatches which feature an AC voltage generator and a time-keeping circuit driven by the power generated therefrom. In wristwatches of this type, a rectifier circuit is needed to convert the alternating voltage produced by the AC voltage generator into a DC voltage for driving the time-keeping circuit. In known wristwatch applications, rectifier circuits performs either half-wave rectification by means of a single diode, or full-wave rectification by means of a bridge employing four diodes arranged in a conventional manner.
However, in forward bias a diode exhibits a voltage drop between its input and output terminals which is slightly greater than the threshold voltage at which current begins to flow in the diode. For silicon junction diodes, this voltage drop may be approximately 0.7 volts, 0.4 volts in the case of a Schottky diode. The voltage supplied to the time-keeping circuit can therefore be as much as 1.4 volts less than the voltage provided by the AC voltage generator, with the result that power is lost. In many circumstances, such as in low-power, low-voltage applications, this power loss becomes significant and undesirable.
In order to overcome this loss, it would in theory be possible to increase the number of turns in the AC generator's coil. However, a coil having a large number of turns is bulky and may be difficult to house in the limited space available in a timepiece of small volume such as a wristwatch. If one were to produce this coil with a wire having a sufficiently small diameter for it not to be bulky, it becomes difficult and costly to manufacture. Increasing the number of turns of the AC generator's coil would also increase the resistance of the coil and hence add to the power loss.
Furthermore, the above-mentioned voltage drop results in a reduction in the energy able to be supplied to and subsequently stored by the time-keeping circuit. If the AC generator is inoperative for any sustained period of time, there is therefore less energy available to drive and maintain the correct functioning of the time-keeping circuit during such periods of inoperability.